Process for the production of suspension polyvinyl chloride suitable for processing by injection molding

Abstract

A suspension polyvinyl chloride is produced which is especially suited for processing by injection molding because it exhibits a greatly improved flowability. Polymerization takes place with an ascending temperature control at at least two different temperatures, a regulator being added to the polymerization mixture by a one-time addition at a conversion of ≧20% by weight and ≦70% by weight.

What is claimed is: 
     
       1. In a process for the production of suspension polyvinyl chloride suitable for processing by injection molding, comprising suspension polymerizing vinyl chloride at at least two polymerization temperatures, subsequent temperature being higher than previous ones, in the presence of an oil-soluble catalyst, a suspension stabilizer, and a regulator, the improvement comprising adding 3-5% by weight based on vinyl chloride of the regulator, said regulator being added to the polymerization mixture in a single addition step, at a point in the polymerization reaction wherein the vinyl chloride conversion is ≧20% by weight and ≦70% by weight. 
     
     
       2. A process of claim 1, wherein the regulator is added to the polymerization mixture at a vinyl chloride conversion of ≧25% by weight and ≦50% by weight. 
     
     
       3. A process of claim 1 wherein the polymerization is conducted in two or more temperature stages, and the polymerization temperature rises after termination of the first stage. 
     
     
       4. A process of claim 3 wherein the polymerization temperature rises stepwise between stages. 
     
     
       5. A process of claim 3 wherein the polymerization temperature rises continuously between stages. 
     
     
       6. A process of claim 1 wherein the polymerization is conducted under continuous temperature increase. 
     
     
       7. A process of claim 3 wherein the polymerization is conducted at two temperature stages, that of the first being 25° to 54° C. and that of the second being 55° to 80° C. and the regulator is added in the first stage. 
     
     
       8. A process of claim 7 wherein the first and second temperatures are 35°-50° C. and 65°-75° C., respectively. 
     
     
       9. A process of claim 7 wherein the rate of temperature change between the initial temperature and the final temperature is 0.01°-5° C./minute. 
     
     
       10. A process of claim 1 wherein after the regulator is added, the temperature increase to the final temperature is conducted at a rate of about 0.01° to 5° C./minute and is effected ≧5 minutes, but ≦15 minutes after adding the regulator. 
     
     
       11. A process of claim 1, 2, 4, 5, 6, 7 or 8 wherein after the regulator is added, the temperature increase to the final temperature is conducted at a rate of about 0.01° to 5° C./minute and is effected ≧5 minutes, but ≦15 minutes after adding the regulator. 
     
     
       12. A process of claim 1 wherein the oil-soluble, free radical initiator is a combination of at least two initiators, their half-life periods being adapted to the selected polymerization temperature stages in such a way that their half-life periods are 1 to 10 hours at each polymerization temperature. 
     
     
       13. A process of claim 7 wherein the temperature rises continuously after termination of the first polymerization stage.